HoldCool=0.1 was inherited from the pre-COOL-state era, where it meant
"eagerly give up active holding and coast" - harmless, since coasting
had no side effects. COOL is a real, actively-controlled state now
(its own pid_cool, reset on every entry), so a threshold this tight
relative to a real heater's discrete power steps (or even just sensor
noise) caused the system to flip in and out of COOL nearly every tick
once resting near a setpoint - resetting both pid_hold's and
pid_cool's integrators each time and never letting either actually
converge.
Confirmed via a full multi-task simulation (real Pot/Sensor/Heater/
TempCtrl tasks, not a simplified loop) of sude/sud_0010.json: 44+
TempCtrl state changes and the run not settling within hours at
HoldCool=0.1, dropping to 8 state changes and a clean 186.5 min finish
at HoldCool=1.0 (matching the other thresholds). This was the dominant
cause of real brews taking far longer than their nominal schedule
duration - not just a forecasting inaccuracy, an actual control-
quality bug.
jens
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